Manufacture of mercury salts



Patented June 2, 1931 UNITED STATES PATENT orricu HUGH S. REID, OF SHAWINIGAN FALLS, QUEBEC, CANADA, AND AYLMER H. MAUDE;

OF NITRO, WEST VIRGINIA, ASSIGNORS TO CANADIAN ELECTRO. PRODUCTS COM- PANY, LIMITED, OF MONTREAL, CANADA '5 Y i MANUFACTURE or MERCURY sAL'rs No Drawing. Original application filed Apri1'18, 1921, Serial No. 462,347,1iow latent No. 1,721,188, and in Canada April 16, 1921. Divided and this application filed July 12,1929. Serial No. 377,910.

I This invention relatesto improvements in the manufacture of salts of mercury, such as the chlorides and sulphates, and is a division from our former application, Serial Number 462,347, file-d April 18th, 1921, matured to Patent No. 1,721,188 dated the 16th July The primary object of the invention is to provide a process by which the salts and particularly the sulphates may be manufactured economically and at a lower temperature than has been hitherto possible.

A further object is to provide a process particularly adaptable to manufacturing salts of mercury from waste products, such as the mercury sludge remaining from the manufacture of acetaldehyde from water and acetylene gas using a mercury salt as catalyst. 1 The accepted process for the manufacture of sulphates ofmercury consists in heating metallic "mercury with concentrated sulphuric acid, the mercury or the acid'being in excess according as a mercuric ,or mercurous sulphate is desired. The temperature necessary tov effect the combination ranges from 190 C. to 210 C. In practice, it is found that a pure sulphate cannot be obtained as 'a mixture of, the mercuric and mercurous sulphates is obtained under all conditions so that separation is necessary. The high temperature necessitates either direct firing-or heating by the circulation of high boiling petroleum. The disadvantages of such a process are first that considerable mercury is lost by volatilization and, secondly, that a great health hazard is incurred when working with mercury at such high temperatures. 1 According to the present invention, sulphates of mercury can-be readily madeat relatively low temperatures, namely, between 20" .C.' and 80. C. by the use of sulphuric acid, preferably diluted, providing there is added tothe reaction a small amount of a suitable catalytic agent such. as nitric acid, nitrous acid, an acid forming oxide of nitrogen or a'nitrate or nitrite, which inthe presence of sulphuric acid converts to nitric or nitrous acid respectively. The nitric acid serves more :or less in a catalytic capacity.

During the reaction nitric oxide is liberated and, by suitably supp-lying oxygen or air to the reaction at atmospheric or super-atmospheric pressure, the nitric oxide is oxidized to remains unchanged but in practice it is found a that a small amount is lost in the form of oxides of nitrogen which escape; 7

When introducing the catalyst in the form of an oxide, it is first dissolved in the sulphuric acid. During the reaction NO fumes are given off and mixed with air or oxygen to oxidize the NO to N0 and the fumes are abs orbe'd in sulphuric acid, thus preparing for the next batch. The sulphuric acid may con tain up to 12% N0 in solution; V

Other salts of mercury such as mercurous chloride may be made in substantially the same manner as the sulphates by using hydrochloric acid instead of sulphuric acid. It has been found that when using small amounts of nitric acid, that is under one-half.

of one percent, the reaction is very feebleif the sulphuric acid is greatly diluted. Thus, while the reaction proceeds at any concentrationof sulphuric acid, itis not as commercially efficient as desirable withless than 25% sulphuric acid, but the rate of reaction increases steadily with the -percentage,ireach{ v ing a maximum eificiency with about sulphuric acid and the rate then decreasing.

The commercially effective range is from 50% to concentration and for thegreat estefliciency between 75% and 85%.

It has also been found that the process is most successfully carried out and bestre sults obtained using sulphuric acid of high concentration, together with a small amount 7 This'wi'll be appreciated from an examina tion" of the following examples. If lower 'concentrationsof sulphuric acid are used the amount of nitric acid must be increased and,

. therefore, for economical reasons, it is adthat is to say, amounts over five percent.

Nitric or nitrousacid is introduced slowly j V and continuously throughout the duration of the reaction or. through substantially the Whole duration unless very low sulphuricconcentrations are used which permit the addition of the nitric acid all,at one time. lVith the more highly concentrated sulphuric acid, it is inadvisable to add the nitric acid except in very smallquantities, since, if any considerable amount is added the reaction becomes so violent that it is very difficult or impossible to control it. M 1 The following examples will serve to illustrate the invention Example I 27 5 lbs. of metallic mercuryis placed in a vessel and 400 lbs. of 85% sulphuric acid and 40 lbs. of water added. To this there is added gradually during two to four hours, approximately 7 lbs. of sodium nitrate or approximately the same weight of 7 2% nitric acid.

On the addition of the nitrate or nitric acid, the reaction commencesand proceeds vigorma the temperaturemaintaining between 40 C. and 60C. Air'is continuously passed through the acid conveniently by circulating a portion ofthe acid through an absorption tower, into the base of which air is blown. The same result may be obtained by blowing air through the acid in the reaction vessel but when this is done there is a certain loss of nitric acid due tolnitri'c oxide being carried away by the escaping air. At the end of from three to four hours, it. will be 1 The process may be carried out as in Ex-- ample'I except that no tower is used a'ndoxyfound that the mercury is completely converted into mercurous sulphate and a. very small amount of'mercuric sulphate. .There remains of the 400 lbs. of 85% acid used,

310 lbs. maybe immediately recovered by sedimentation and is available'jt'or re -use, ap-

proximately lbs. being i'x d the sulphate. a V.

In carrying out the process according to this example, the amount of sulphuric acid used may be reduced to 275 lbs. if desirechthe amount of water being proportionally reduced. V I

V Ewampl e ll gen is blown into the reaction mixture to oxidize the nitric oxide to-nitrogen peroxide.

The invention is particularly applicable to the recoveryof mercury from a process such as the manufacture of acetaldehyde, in which the mercury is not obtained as a metallic regupa d with previous exam v V about 380 lbs. of'80%acidlof; which u V 'lus but as a finely divided precipitate containing impurities suchas complex mercury organic compounds. I or the recovery of mercury from such material, the sludge is first settled and the liquid removed by decantation, leaving a moist mercury sludge.

V Emamplelll 1 that the sludge already containsfrom 15% to r 25% of water. Sodium nitrate or nitric acid is added as in Example I, the amount varying from 11 lbs. to 17 lbs; according to the com position of thesludge. The temperature is maintained at approximately 50 by the heat of reaction and the results obtained are sub- .stantially as in Example I. The sludge frequently contains a certain amount of impurity which gives of]? sulphur dioxide and this acts to reduce the nitric oxide. vIt may therefore be'advisable when working with the sludge to add the sulphuric acid tothe sludge before introduction of the nitric acid, so that the sulphurdioxide is largely driven off at the commencement and the reduction of nitric acid minimized to aconsiderable extent. i

' 7 Example IV V 5 v kilos. of mercury sludge containing/approximately 50% mercury and 25% water. is placed in a suitable vesseland 1.2 kilos. of 94% sulphuric acid added. Sodium nitratefis added from time to 'time, the total amount ranging between 75 'grms. and 115 grms. Oxygen under a pressure of approximately 2"atm'ospher'es absolute is passed into the re- Ewamplc V; 7

' 5'kilos. of'sludge, containing 50% mercury and 25% water, is placedin'a reaction vessel and 1 :2 kilos; of 94% sulphuric acid containing N0 insolution up to 12% is added slowly during the course of reaction. The oxides of nitrogen evolved are drawn ofi' together with a good supply of air and passedthrough 94% sulphuricacid. This acid absorbs all the nitric oxidean-d is used next charge. v y

For reasons of economy, it is advisable to 'add nitric ac'idto the reaction in theforniof sodium nitrate, but forthe'sake of. convenience nitriclacid'be used as it maybe 12 over again for the easily added a little; at a time as the'reaction proceeds.

. y The. present" process presents advantages perature is low enough so that very little volatilization of the mercury occurs and the health of the operators is little, if any, affected. The comparatively low temperatures of the reaction are easily maintained by the heat of reaction itself, so that no external heating is necessary. The vigor of the reaction and therefor the heat thereof may be controlled by the rate of addition of the nitric acid. It will be seen from the foregoing examples that a smaller amount of nitric acid will suffice when using metallic mercury. hen mercuric sulphate is desired, greater amounts of sulphuric and nitric acids are used than given in the examples. It will also be found that when the process is operating smoothly a somewhat less amount of sulphuric acid than specified may be used without affecting the results.

The body essential to the success of the present invention is nitric or nitrous acid, which for the purposes of this invention are equivalents, and it is to a large extent immaterial in what manner the acid is introduced. The acid may be introduced as such or as an acidforming oxide or as a suitable salt, which in presence of the sulphuric acid liberates the desired catalytic agent. It will therefore be understood that the addition of acid-forming nitrogen oxides and suitable salts is the full equivalent of adding nitric or nitrous acid. In the case of the manufacture of sulphates the acid salts of sulphuric acid may be used instead of the normal acid. The reaction proceeds at any temperature from ordinary room temperature upward and with anv concentration of acid but, with weak acid solutions, the reaction approaches efficiency only when com paratively high temperatures are maintained. It is also necessary when working with weak acid solutions to employ larger amounts of catalyst in order to expedite the reaction, especially if the tempertaure is low. As the temperature of the reaction is maintained ordinarily by the heat of reaction and as the vigor of the reaction depends upon the amount of catalyst, it will be seen that the temperature may be regulated by judicious additions of the catalytic agent.

Having thus described our invention, what we claim is 1. A process of making salts of mercury, which comprises bringing together metallic mercury and a strong non-oxidizing mineral acid of less than 60% concentration in pres ence of nitric acid.

acid of less than 60% concentration in presence of nitric acid, and supplying oxygen to the reaction mixture during the reaction to regenerate nitric acid.

4. A process of making a sulphate of mercury, which comprises bringing together metallic mercury and sulphuric acid of less than 60% concentration in presence of nitric acid.

our hands.

HUGH S. REID. AYLMER H. MAUDE.

2. A process of making salts of mercury, V 

